Testing with the SATRA Pedatron

Exploring the mechanics and laboratory use of this key footwear test machine.

This article provides a brief introduction to the SATRA STM 528 Pedatron – the world’s most advanced and realistic walking simulator for footwear. Here we explain the development, workings and use of this key test machine to conduct evaluations of whole footwear, materials and components in a reduced time.

Traditionally, there are two ways to assess the wear resistance of footwear soling. An actual wear trial can be conducted, but this requires a number of wearers and several months of actual wear. It has become harder to conduct these over the years due to liability legislation, and seasonal weather is a challenge to repeatability. Alternatively, a fairly quick and standard test in the laboratory can be carried out, but this will naturally lack the organic nature of a subject-based test.

Pedatron provides an accelerated wear simulation under realistic conditions. This tester combines the realism of a service trial with the speed of the laboratory test and overcomes the drawbacks of both. It does this by simulating a true walking action over a real wear surface, with motions, speeds and forces that reproduce values obtained in biomechanical studies.

Realistic walking action

The machine was originally conceived as a whole footwear sole abrasion device. Through many years of honing, it is now utilised to artificially wear footwear and even to test the durability of electronics in footwear. The textured concrete slab normally used is a demanding but very realistic surface.

The machine’s test program recreates alternate straight steps and turning steps, in which the sole forepart is in contact with the slab. The combined action of walking and the turning of the wear surface produces results that correlate closely to those that are found in wear trials, with the added advantage that the result is completely repeatable. Irrespective of harsh winters and hot summers, Pedatron is capable of performing exactly the same task.

With regard to the aspect of simulation, Pedatron actually replicates the forces present in real wear. It uses the mass of a real person to create friction between the surface and the footwear complete with locomotory and torsional forces, and is calibrated with the same equipment that is used to measure real human gait. A typical test programme can consist of as little as 12,000 steps – taking about six hours – although this can be extended if necessary.

In its role as a biomechanical sole abrasion machine, the mass loss over a number of steps can be measured and compared with a similar sole that has been manually scoured into a worn-out condition. The lifetime of the sole can therefore be determined in terms of ‘steps’. SATRA uses the simple formula of 1,000 steps to a mile. The machine can be used to visually investigate the wear of tread pattern elements, the integrity of inserts and any unusual wear behaviour. It will also condition the surface of a soling prior to slip resistance testing in the worn condition.

When a Pedatron test is conducted, a flexible and compressive prosthetic foot form fills the interior of the shoe. This representation of the foot produces realistic pressures inside the footwear and allows for a natural movement (creating friction and torsional forces). It provides a good indication of the durability of underfoot components in addition to the sole, such as footbeds, midsoles and the ribs in cavity units).

Testing on footbeds has revealed that it is quite a challenge to tell an actual used footbed from one worn on Pedatron. Further tests can then be conducted, such as for shock absorption, cushioning properties and sole bonds. The advantage when assessing these components is that they are tested in the context of completed footwear, so the effect of the components acting together in a simulated walking situation is evaluated. If the footwear is then re-engineered, the exact same wear programme can be repeated, unlike subject-based wear trials.

A reliable workhorse

From its early days as a research test machine, the STM 528 Pedatron has evolved into a reliable and effective test machine, capable of running continuously for 24 hours a day. Operating a Pedatron is not labour intensive. Apart from setting up the test initially and inspection of the test samples at the end of blocks of testing cycles, the machine can be allowed to run unsupervised.

Latest developments include varying of the loads and heel and toe angles. In addition, the walking surface can be mounted on a small gradient to produce a slightly different contact angle on every step, giving a much-improved organic-looking wear pattern. As already mentioned, it is often used to test the integrity and durability of footwear containing electronics, a test that is often combined with the addition of moisture into the footwear.

Publishing Data

This article was originally published on page 16 of the October 2024 issue of SATRA Bulletin.

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